Temperature control alarm system

ABSTRACT

As described herein, a temperature alarm control system is provided which includes a plurality of temperature measuring devices which generate positive or negative signals in accordance with an increase or decrease in temperature in a corresponding number of furnaces to which the devices are operatively connected. The signals are amplified and thereafter, of the signals developed by the measuring devices, only the positive and negative signals having the greatest magnitudes are supplied to an alarm circuit to excite a pair of alarms.

United States Patent Harris 1 Jan. 18,1972

211 App]. No.: 779,768

Primary Examiner-John W. Caldwell Assistant Examiner-Scott F. PartridgeAttorneyBrumbaugh, Graves, Donohue & Raymond [52] US. Cl ....340/228,328/3, 340/233 [57] ABSTRACT [51] Int. Cl ..Glk 7/24, GOlk 7/l6 [58]Field Search 340/227 228 233 213 248 A As described herein, atemperature alarm control system lS B provided which includes aplurality of temperature measuring devices which generate positive ornegative signals in ac- 56] References Cited cordance with an increaseor decrease in temperature in a corresponding number of furnaces towhich the devices are UNITED STATES PATENTS operatively connected. Thesignals are amplified and thereafter, of the signals developed by themeasuring devices, 3,191,068 6/1965 Robb, Jr. ..340/233 X only thepositive and negative Signals having the greatest 3,304,441 2/1967nitudes are supplied to an alarm circuit to excite a pair of 3,404,313/1968 Happel et a] ..317/40 X alarms 3,452,656 7/1969 Ruhle et al.....340/233 X 3,494,196 2/1970 Moussette ..340/233 X 7 Claims, 1 DrawingFigure 4 m #4 144 K l 23 4 3%: Kai/gift i 342 ADJUST //a% g 2 7 44FURNACE HIGH /!g ALARM CIRCUIT 4 a M g! a- 3% FURNACE W! LOW A?! ALARMCIRCUIT 7 TRIGGER LEVEL ADJUST, FURNACE ,,z4

POWER ,2;

SUPPLY TEMPERATURE CONTROL ALARM SYSTEM BACKGROUND OF THE INVENTION Thisinvention relates to alarm systems and, more particularly, totemperature control alarm systems which provide alarm indications whenthe actual temperature in a particular environment, such as a furnace,deviates from a predetermined temperature.

In presently devised temperature control systems which provide highlyprecise measurements of temperature, instead of measuring an inputsignal which corresponds to the actual temperature in a furnace or thelike directly on a meter or a similar device, an opposing signal isgenerated. The magnitude of this opposing signal is increased ordecreased, as the case may be, until its magnitude corresponds to themagnitude of the input signal to cancel the input signal and achieve anull or balanced condition. The magnitude of the opposing signal isdeterminative of the temperature in the furnace or the like.

In alarm systems embodying the above-described control systems, alarmsare coupled to the control systems and are actuated whenever themagnitude of the opposing signal is above or below certain selectedlevels. This indicates that the deviation of actual temperature fromdesired temperature has reached a certain value which requires instantattention. Heretofore in such systems, an alarm has been associated witheach of the temperature control systems. This gives rise to a rathercomplex overall alarm system in that each of the alarms requirespresetting to meet the exigencies of the particular environment withinwhich its associated temperature control system is situated.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a temperature control alarm system wherein thetemperatures in a plurality of locations can be effectively monitoredand a single alarm actuated when any one of the systems generates asignal to indicate that the deviation between the actual temperature andthe desired temperature in one of the locations has reached a criticalvalue.

This and other objects are accomplished by the temperature control alarmsystem of the present invention which comprises a plurality oftemperature-measuring devices for generating positive or negativesignals in accordance with an increase or decrease in temperature in acorresponding number of selected locations to which the devices areoperatively connected. Also provided are a corresponding plurality ofunidirectional current conducting devices responsive to the signalsgenerated by the measuring devices and having common output terminalsconnected together and to the input terminals of a pair of alarmcircuits. By connecting the output terminals of the unidirectionalcurrent conducting devices together, only the positive and negativesignals having the greatest magnitudes are supplied to the alarmcircuits to excite the alarms.

In thepreferred embodiment of the invention, each temperature-measuringdevice comprises a wheatstone bridge having one leg thereof comprising atemperature-sensitive device situated in a heat-generating plant andhaving a second leg which includes a variable impedance. The variableimpedance is set to a value which relates to the value of thetemperature-sensitive device such that a balanced condition in thebridge is reached when the temperature-sensitive device has a valuewhich reflects a desired temperature in the heatgenerating plant. Whenthe temperature in the plant rises or falls above or below the desiredtemperature, an imbalance is created and the bridge developes a positiveor negative signal. This signal, which may be amplified, is suppliedfrom the bridge to a pair of diodes connected in parallel and forwardbiased and reverse biased, respectively. The diodes will conduct eitherof the signals provided signals having greater magnitudes are notconducted by the diodes associated with any of the othertemperature-measuring devices.

BRIEF DESCRIPTION OF THE DRAWING In the Drawing: 7

FIG. 1 is a schematic block diagram of a typical temperature controlalarm system arranged according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In a typical temperature controlalarm system arranged according to the present invention, as shown'inFIG. 1, the temperatures in a plurality of furnaces 10a-l0n are measuredand an alarm sounded when the temperature in any one ofthe furnacesexceeds or falls below a predetermined desired temperature. Mounted inthe furnaces 1012-1011 are temperaturesensitive devices 1211-1211, whichmay, for example, be platinum resistance thermometers and which comprisethe first legs of a corresponding plurality of wheatstone bridges1411-14. A plurality of conductors 1611-1611 couple thetemperature-sensitive devices 1211-1211, respectively, to the bridges1411-1411.

The second legs 1811-1811 of the wheatstone bridges 1411-14 compriserheostats which may be adjusted to create a "al balans san i a n th brie ,4- 1m cally, the remaining legs 2011-2011 and 2211-2211 of thewheatstone bridges comprise resistors having fixed resistances. As isunderstood in the art, in order to achieve a balanced condition in thewheatstone bridges 1411-1411. it is necessary that the ratio between theresistance values of the temperaturesensitive devices 1211-1211 and therheostats 1811-1811 equal the ratio between the values of theresistances 2011-2011 and 22a-20. The necessary relationship is givenbelow:

R12a 129 RZOa-ZOn R 18a 18 1 1122 42 Coupled to the input terminals ofthe wheatstone bridges 1411-14 via a pair of conductors 24 is a powersupply 26 which supplies a constant DC voltage to the bridges. Theoutput terminals of the bridges 1411-14n are connected via conductors2811-28n to the input terminals of a corresponding plurality ofamplifiers 30a-3011.

As above-mentioned, the rheostats 1811-18n are adjusted such that a nullcondition or balanced condition is reached in the bridges 1411-1411 whenthe temperatures within the furnaces 1011-1011 are within selected andpreferred ranges. Obviously, the desired temperature or temperaturerange for each of the furnaces 1011-10n may be the same or may bedifferent. When the temperatures in the furnaces 1011-1011 increaseabove the desired degrees of hotness, imbalances are created and thebridges 1411-1411 develop positive DC voltage signals. This is trueinasmuch as the resistance values of the devices 1211-12 increase as thetemperatures in the furnaces 1011-1011 increase. Conversely, as thetemperatures within the furnaces 1011-10 decrease, the resistance valuesof the devices 1211-12 decrease and the bridges 1411-1411 developnegative DC signals and supply these signals to the amplifiers3011-3011.

The signal carrying output terminals of the amplifiers 3011-30 areconnected to a corresponding number of forward biased diodes 3211-3211and reverse biased diodes 3411-3411, respectively, connected inparallel. The common output terminals of the amplifiers 3011-3011 areconnected together via a conductor 36 and to the input terminals ofapair of amplifiers 38 and 40. The cathodes of the forward biased diodes32a-32 are connected together via a conductor 42 and connected to theother input terminal of the amplifier 38. A conductor 44 connects theanodes of the reverse biased diodes 3411-34 together and to the otherinput terminal of the amplifier 40. The diodes 32a-32n and 34a-34n,which may be, for example, silicon diodes, conduct when the voltagelevels thereacross exceed, for example, three-quarters of a volt.

As is understood, of the diodes 32a-32n and 34a-34n, only one forwardbiased diode and one reverse biased diode will conduct at a time becausethe diode conducting the highest current signal will back-bias thediodes to which it is con nected. For example, should the diode 32aconduct the highest positive current signal, that signal will back-biasthe diodes 32b-32n and render them nonconductive. Similarly, if thediode 34b were to conduct the highest negative current signal, thatsignal would back-bias the remaining diodes 34a, 34c34 and render themnonconductive. It will be noted that one of the diodes 32a-32n will berendered conductive when there is a predetermined increase intemperature in oneor more of the furnaces 10a-l0r| and one of the diodes34a34n will be rendered conductive when there is a predetermineddecrease in temperature in one or more of the furnaces la-l0.

Coupled to the amplifier 38 is a trigger level adjust circuit 46 whichadjusts the triggering input level of the amplifier. Similarly, atrigger level adjust circuit 48 is coupled to the amplifier 40 foradjusting the triggering input level of the amplifier. The adjustcircuits 46 and 48 are provided to control the amount of temperaturevariation which will set an alarm. Specifically, any one of the diodes32a-32n or 34a-34n may conduct, for example when the deviation voltagedeveloped by one of the bridges l4a-l4n represent a 2 variation in oneof the furnaces from the desired temperature. If it is not desired toset the alarm for a 2 variation but rather a 16 variation, the adjustcircuits 46 and 48 are adjusted to set the amplifiers 38 and 40 torespond to signals having magnitudes which correspond to a 16 deviationin temperature.

The output terminals of the amplifier 38 are connected to a high alarmcircuit 50 which for example, may be a solenoidactuated bell, andaccordingly, produces a loud ringing noise whenever the temperature inone of the furnaces exceeds a fixed or desired degree of hotness by apredetermined amount. A low alarm circuit 52 is coupled to the outputterminals of the amplifier 52 and provides a ringing noise of differentpitch or loudness level whenever the temperature in one of the furnacesl0a-l0n falls below a desired degree of hotness.

In operation, the rheostats l8a-18n of the wheatstone bridges 14a-l4nare adjusted such that a balanced condition exists when a desiredtemperature is realized in the furnaces l0a-l0, as reflected by theresistance values of the temperature-sensitive devices l2a-l2n locatedin the furnaces. With balanced conditions, no signal is supplied fromthe wheatstone bridges 140-1411 to the amplifiers 30a-30n. As soon asthe temperature in any one of the furnaces l0a-l0n increases ordecreases to bring about an imbalance in its corresponding wheatstonebridge, the corresponding amplifier will supply either a positive ornegative output signal. For example, if the temperature in the furnace bwere to increase above a predetermined degree of hotness, the amplifierb would supply a positive signal through the diode 32b to the inputterminal of the amplifier 38. Depending upon the setting of the triggerlevel adjust circuit 46, the amplifier 38 would then set the high alarmcircuit 50 and an alarm would be sounded. If at the same time, thetemperature in the furnace 12n were to decrease below a desired degreeof hotness, the wheatstone bridge 1411 would become unbalanced and theamplifier 30!: would supply a negative signal through the diode 34n tothe amplifier 40. The amplifier 40, depending upon the setting of thetrigger level adjust circuit 48, would then activate the low alarmcircuit 52 and a second alarm would be sounded.

If the temperatures in all the furnaces l2a-12n were to increase abovedesired degrees of hotness, all the amplifiers 3011-30 would generatepositive signals. However, only the signal having the greatest magnitudewould be conducted so that only it would implement the setting of analarm, the remaining diodes being rendered nonconductive. Similarly, ifthe temperatures in the furnaces 10a-10n were to decrease below desireddegrees of hotness, the amplifiers 30a-30n would conduct, but only thenegative signal having the greatest magnitude would be passed by one ofthe diodes 3411-34 to the input terminal of the amplifier 40 to set thelow alarm circuit 52.

Although the invention has been described herein with reference to aspecific embodiment, many modifications and variations therein willreadily occur to those skilled in the art. For example, instead ofemploying a wheatstone bridge as the temperature-measuring device,thermocouples could be employed. In this instance, the input voltagesignals corresponding to the temperatures in the furnaces, would besummed with locally generated signals from precision voltage dividers.Accordingly, all such modifications and variations are included withinthe intended scope of the invention as defined by the following claims.

I claim:

1. A temperature control alarm system comprising a plurality oftemperature-measuring devices responsive to temperature deviations abouta nominal temperature in a corresponding plurality of locations forgenerating positive and negative signals having amplitudes correspondingto the extents of said deviations, means responsive to the positive andnegative signals generated by the plurality of temperature-measuringdevices for conducting the positive and negative signals having thegreatest magnitudes, an alarm means selectively responsive to theconducted positive and negative signals for providing indications thattemperature deviations have occurred in at least one location and alarmlevel control means operatively coupled to the alarm means forcontrolling the levels at which the alarm means, in response to theconducted positive and negative signals, provides indications thattemperature deviations deviating from the nominal temperature by aselected amount have occurred in at least one location.

2. A temperature control alarm system according to claim 1 furthercomprising amplifier means responsive to the positive and negativesignals generated by the plurality of temperaturemeasuring devices foramplifying said signals and supplying said signals to the conductingmeans.

3. A temperature control alarm system according to claim 1 wherein theplurality of temperature-measuring devices comprise a plurality ofwheatstone bridges, each bridge comprising at least one leg thereofincluding a temperature-sensitive device located in a particularlocation and a second leg thereof including means for providing avariable impedance to balance the bridge when the temperature-sensitivedevice has a predetermined impedance.

4. A temperature control alarm system according to claim 1 wherein thealarm means comprises a high alarm circuit responsive to a conductedpositive signal for providing an indication that a positive deviation intemperature has occurred in at least one location and a low alarmcircuit responsive to a conducted negative signal for providing anindication that a negative deviation in temperature has occurred in atleast one location.

5. A temperature control alarm system according to claim 4 wherein theconducting means comprises a plurality of diode circuits operativelycoupled to the plurality of temperaturemeasuring devices, each diodecircuit comprising a pair of diodes connected in parallel and forwardand reverse biased, respectively, and the corresponding output terminalsof the diode circuits are connected together and to the input terminalsof the high alarm circuit and the low alarm circuit, respectively.

6. A temperature control alarm system according to claim 1 wherein theplurality of temperature-measuring devices are responsive to temperaturedeviations in a corresponding plurality of furnaces.

7. A temperature control alarm system according to claim 1 wherein theplurality of temperature-measuring devices comprise a plurality ofthermocouples.

2272 23 UNITED STATES PATENT ()FFICE CERTIFICATE OF CORRECTIQN PatentNo. 3'636"54o I Dated January 1972 ven ofls) I Holton E. Harris 4 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column '2, llne l8, "14" should be ----l'4n'- line 22, "-14" should be--1-4H--; line 32, "20" should be --2-2H--; line 37, "14" should be--l4:T-; line 52, "12" should be -l'2--; line 55, "10" should be--l'0n--; line 56, "12'' should be -.-1"2E-; line 59, "30" should be'-3'0E---; line 66, 1'32"v should be '-32r 1'--; line 69, "34" should be--3'4r y--; Column 3, line 7, "34" should be '--3'41 line l3, "10"should be --l0 line 41, "10" should be -l'0g-; line 64, "30" should be-30 Column 4, line 2, "34" should be --34r 1 Signed and sealed this 18thday of July 1972.

(SEAL) Attest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attesting Officer Comissioner ofPatents

1. A temperature control alarm system comprising a plurality oftemperature-measuring devices responsive to temperature deviations abouta nominal temperature in a corresponding plurality of locations forgenerating positive and negative signals having amplitudes correspondingto the extents of said deviations, means responsive to the positive andnegative signals generated by the plurality of temperature-measuringdevices for conducting the positive and negative signals having thegreatest magnitudes, an alarm means selectively responsive to theconducted positive and negative signals for providing indications thattemperature deviations have occurred in at least one location and alarmlevel control means operatively coupled to the alarm means forcontrolling the levels at which the alarm means, in response to theconducted positive and negative signals, provides indications thattemperature deviations deviating from the nominal temperature by aselected amount have occurred in at least one Location.
 2. A temperaturecontrol alarm system according to claim 1 further comprising amplifiermeans responsive to the positive and negative signals generated by theplurality of temperature-measuring devices for amplifying said signalsand supplying said signals to the conducting means.
 3. A temperaturecontrol alarm system according to claim 1 wherein the plurality oftemperature-measuring devices comprise a plurality of wheatstonebridges, each bridge comprising at least one leg thereof including atemperature-sensitive device located in a particular location and asecond leg thereof including means for providing a variable impedance tobalance the bridge when the temperature-sensitive device has apredetermined impedance.
 4. A temperature control alarm system accordingto claim 1 wherein the alarm means comprises a high alarm circuitresponsive to a conducted positive signal for providing an indicationthat a positive deviation in temperature has occurred in at least onelocation and a low alarm circuit responsive to a conducted negativesignal for providing an indication that a negative deviation intemperature has occurred in at least one location.
 5. A temperaturecontrol alarm system according to claim 4 wherein the conducting meanscomprises a plurality of diode circuits operatively coupled to theplurality of temperature-measuring devices, each diode circuitcomprising a pair of diodes connected in parallel and forward andreverse biased, respectively, and the corresponding output terminals ofthe diode circuits are connected together and to the input terminals ofthe high alarm circuit and the low alarm circuit, respectively.
 6. Atemperature control alarm system according to claim 1 wherein theplurality of temperature-measuring devices are responsive to temperaturedeviations in a corresponding plurality of furnaces.
 7. A temperaturecontrol alarm system according to claim 1 wherein the plurality oftemperature-measuring devices comprise a plurality of thermocouples.